title: Pd-catalyzed carbonylation of diazo compounds at atmospheric pressure: a catalytic approach to ketenes.
abstract: The carbonylation of carbenes through catalytic cycles is highly desirable due to the importance of ketene-mediated reactions in organic synthesis. In this investigation, a highly efficient and mild catalytic approach toward ketene intermediates has been developed based on Pd-catalyzed carbonylation of diazo compounds with CO. When α-diazocarbonyl compounds or N-tosylhydrazone salts are heated in the presence of a palladium catalyst under atmospheric pressure of CO, ketene intermediates are formed in situ, where they undergo further reactions with various nucleophiles such as alcohols, amines, or imines. The Pd-catalyzed tandem carbonylation-Staudinger cycloaddition gives β-lactam derivatives in good yields with excellent trans diastereoselectivity. The results from DFT calculation on the reaction mechanism suggest that Pd is involved in the [2 + 2] cycloaddition process and affects the diastereoselectivity of the β-lactam products by assisting isomerization of the addition intermediate. On the other hand, the acylketenes generated from the Pd-catalyzed carbonylation of α-diazoketones react with imines in a formal [4 + 2] cycloaddition manner to afford 1,3-dioxin-4-one derivatives. This straightforward carbonylation provides a new approach toward highly efficient catalytic generation of ketene species under mild conditions.
authors.affiliation: Beijing National Laboratory of Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China.
authors.forename: Zhenhua
authors.initials: Z
authors.lastname: Zhang
authors.forename: Yiyang
authors.initials: Y
authors.lastname: Liu
authors.forename: Lin
authors.initials: L
authors.lastname: Ling
authors.forename: Yuxue
authors.initials: Y
authors.lastname: Li
authors.forename: Yian
authors.initials: Y
authors.lastname: Dong
authors.forename: Mingxing
authors.initials: M
authors.lastname: Gong
authors.forename: Xiaokun
authors.initials: X
authors.lastname: Zhao
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Jianbo
authors.initials: J
authors.lastname: Wang
mesh_terms: D001274:Atmospheric Pressure; D001391:Azo Compounds / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D003500:Cyclization; D005030:Ethylenes / Q000138:chemical synthesis* / Q000737:chemistry; D007659:Ketones / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D001391:Azo Compounds; D005030:Ethylenes; D007659:Ketones; D009942:Organometallic Compounds; D010165:Palladium; C008223:ketene